5.4-stable review patch. If anyone has any objections, please let me know.
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From: Maciej Fijalkowski maciej.fijalkowski@intel.com
[ Upstream commit e37084a26070c546ae7961ee135bbfb15fbe13fd ]
i40e has a feature which writes to memory location last descriptor successfully sent. Memory barrier in i40e_clean_tx_irq() was used to avoid forward-reading descriptor fields in case DD bit was not set. Having mentioned feature in place implies that such situation will not happen as we know in advance how many descriptors HW has dealt with.
Besides, this barrier placement was wrong. Idea is to have this protection *after* reading DD bit from HW descriptor, not before. Digging through git history showed me that indeed barrier was before DD bit check, anyways the commit introducing i40e_get_head() should have wiped it out altogether.
Also, there was one commit doing s/read_barrier_depends/smp_rmb when get head feature was already in place, but it was only theoretical based on ixgbe experiences, which is different in these terms as that driver has to read DD bit from HW descriptor.
Fixes: 1943d8ba9507 ("i40e/i40evf: enable hardware feature head write back") Signed-off-by: Maciej Fijalkowski maciej.fijalkowski@intel.com Reviewed-by: Aleksandr Loktionov aleksandr.loktionov@intel.com Tested-by: Rinitha S sx.rinitha@intel.com (A Contingent worker at Intel) Signed-off-by: Tony Nguyen anthony.l.nguyen@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ethernet/intel/i40e/i40e_txrx.c | 3 --- 1 file changed, 3 deletions(-)
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c index 6067c88668341..ff213cbe84ca8 100644 --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c @@ -794,9 +794,6 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi, if (!eop_desc) break;
- /* prevent any other reads prior to eop_desc */ - smp_rmb(); - i40e_trace(clean_tx_irq, tx_ring, tx_desc, tx_buf); /* we have caught up to head, no work left to do */ if (tx_head == tx_desc)